This section of the report will provide a rolling three month update on a monthly basis of the state of the climatic and ecological indicators used in monitoring areas at risk to RVF activity. These indicators include, global SST anomalies patterns, Equatorial Western Indian Ocean (WIO) and Eastern Pacific Ocean (EPO: NINO 3.4) SST anomalies, Southern Oscillation Index (SOI) and Outgoing Longwave Radiation (OLR) anomalies, Rainfall and anomalies, Normalized Difference Vegetation index anomalies and RVF risk map for Africa and the Arabian Peninsula.
1. SOI and SST Indices
The SOI index continued to tumble with a value of -1.1 in July from -0.6 in June, suggesting a strengthening of El Niño conditions. This is supported by continued anomalous increase in positive SSTs in NINO 3.4, NINO 4 and NINO1&2 monitoring regions which have tremendously warmed over the last two months with values of +1.67°C, 1.0°C and 2.87°C respectively in July. The western Indian Ocean basin has continued the warming pattern with the WIO SST index at +0.56°C in July from +0.40°C in June indicating continued warmer than normal conditions over this ocean basin. The persistent above-average sea surface temperatures (SST) (below) in the central equatorial Pacific region indicate that El Niño conditions are present and significantly strengthening. Enhanced convection is amplified over the central and eastern equatorial Pacific and suppressed convection over the Indonesian basin is fully entrenched. Collectively, these atmospheric and oceanic features reflect an ongoing and strengthening El Niño conditions. Currently a majority of model forecasts predict El Niño conditions (90% chance) through Northern Hemisphere winter 2015-16, and around an 85% chance it will last into early spring 2016. The current conditions will continue to strengthen and last through the rest of 2015 with a favorable chance of a strong warm event. The consensus forecast is for a significant El Niño in excess of +1.5°C in the Niño-3.4 region(3-month values of the Niño -3.4 index +2.0°C or greater) during the peak period in December - January. In some locations, certain impacts often associated with El Niño may appear during the Northern Hemisphere through the summer 2015 season.
Cumulative NDVI anomalies for Africa for May 2015 to July 2015 still show positive anomalies concentrated in South Sudan, northwestern and eastern Ethiopia, Somalia and parts of eastern Kenya. The RVF risk map below was derived from thresholding NDVI anomaly data to detect areas persistent of above normal NDVI. Periods of widespread and prolonged heavy rainfall lead to flooding of dambos and anomalous green up in vegetation, creating ideal ecological conditions for the emergence RVF vectors. For the period May 2015 to July 2015, the RVF persistence model identifies areas in South Sudan and eastern Ethiopia, and isolated parts of central Somalia where ecological conditions would support the emergence of RVF vectors. Enhanced surveillance is advised in these areas especially in the next three months (September October and November 2015). The above normal rainfall conditions could lead to outbreaks of other vector and water-borne diseases elsewhere.